This invention relates an improved apparatus for the transportation and storage of high plutonium content transuranic waste. In particular, Applicants' apparatus allows for the shipment and storage of transuranic waste at a rate 8.6 times greater than is available using currently available technology. Employing a TRUPACT-II, type B external container, in conjunction with currently available interior containers only 325 Fissile Grams Equivalent(FGE) can be shipped to an approved tranuranic waste repository in a single TRUPACT-II container. Using Applicants' inner container in conjunction with the TRUPACT-II, 2800 FGE can be shipped to an approved nuclear waste storage site per TRUPACT-II container. In addition, Applicants' container provides additional radiation shielding for the handling of wastes with high Americium-241 (Am241) content.
Applicants' container was approved for use in the TRUPACT-II shipping container by the Nuclear Regulatory Commission in 1997 for the handling of wastes. The container was subsequently evaluated and approved for storage of highly dispersible TRU wastes and residues.
The initial accident testing of the TRUPACT-II shipping container showed that the lids of the drums contained in the container could come off during a hypothetical accident and allow the contents of the drum to lose spacing control from a criticality standpoint. Based on this possibility, and the appropriate worst case assumptions, a TRUPACT-II criticality limit of 325 FGE was calculated. The Pipe Component, contained in Applicants' Pipe Overpack Container was designed and tested to maintain containment of its contents during normal transport and hypothetical accident conditions. The criticality calculations crediting the Pipe Component showed that the criticality requirements were met, thus, increasing the limits of the TRUPACT-II to 2800 FGE.
The Pipe Overpack Container system, which includes the Pipe Component as its central feature, was designed, tested, and qualified as a Nuclear Regulatory Commission approved, enhanced TRUPACT-II payload container. Applicants' apparatus in conjunction with the TRUPACT-II system allows for more efficient transport and disposal of certain residues and wastes at an appropriate waste disposal sites.
The following benefits occur from the use of the Pipe Overpack Container:
Increased criticality limits for the TRUPACT-II Type B shipping container. Up to fourteen Pipe Overpack Containers can be shipped in a TRUPACT-II. Each container may have a maximum fissile gram equivalent loading of 200 grams, for a total TRUPACT-II load of 2800 FGE. For shipments of waste packaged in payload containers other than the Pipe Overpack Container, the limit is 325 FGE per TRUPACT-II. PA1 The Pipe Overpack Container provides for radiation shielding for high Americium-241 content transuranic wastes. PA1 Use as a structurally enhanced system for the storage of highly dispersible materials containing plutonium. PA1 Three top-impact drop tests were performed. In each test, two drums were strapped end-to-end as if positioned for transport within a TRUPACT-II. Top impact tests were performed for the following configurations of overpacks: PA1 Two 55 gallon drums containing 6 in diameter pipe components; PA1 Two 55 gallon drums containing 12 in diameter pipe components; PA1 Two 55 gallon drums: one containing a 6 inch diameter pipe component and one containing a 12 inch diameter pipe component. PA1 One side impact test was performed by dropping an uncertified but functional TRUPACT-II Inner Containment Vessel (ICV) with a payload assembly. The payload assembly consisted of a top layer of seven Pipe Overpack Containers containing 6 inch diameter pipe components and a bottom layer of seven Pipe Overpack Containers containing 12 inch diameter pipe components. This drop demonstrated a worst case, as damage to the Pipe Overpack Containers would be less severe within the entire TRUPACT-II package, which includes ten inches of impact-absorbing foam. PA1 A dynamic crush test of the Pipe Overpack Container was performed where the container was placed on an unyielding target, and a 500 kg steel plate 1 m square was dropped from 30 ft height onto the package. The test was performed with the container in an upright orientation as it is the orientation they will be in during storage, and the test was designed to simulate loading on the container if the roof of the storage building were to collapse onto the package. PA1 A bare Pipe Component drop test was performed. This test consisted of dropping bare inner Pipe Components onto an essentially unyielding target from a height of 10 ft. The tests were performed with the bolted closure of the pipe impacting the target first. The tests were performed to simulate a handling accident in which the pipe is dropped prior to being placed within the overpack. The test also demonstrated safety for a scenario where the interim storage of the pipes in racks without the protective overpack. PA1 The final test was an engulfing pool fire test. In this test four Pipe Overpack Containers were placed on an open support stand with 1 m spacing between them in a square array. The bottom of the units were 1 m above the surface of a 10 square meter pool of jet fuel floating on top of a layer of water. The fuel was ignited and allowed to burn for 30 minutes. This type of fire test generally results in a flame temperature between 1073 K and 1373 K. The test was performed to simulate a fire in a storage building. Two designs of drum filters were tested in the fire: A stainless steel housing--carbon media filter, and a polyethylene housing--carbon filter media filters. PA1 Elimination of the 55 gallon drums, packing material, and any cans used inside the Pipe Components as migration barriers; PA1 Uniform distribution of water moderator in the waste; PA1 Closely packed geometry of fourteen Pipe Components without the presence of any other material; PA1 Flooding of the TRUPACT-II with the moderation medium; PA1 Reflection of escaping neutrons into the system.
A test program was developed and implemented to demonstrate the integrity of the Pipe Overpack Container under hypothetical transportation accident conditions. Normal conditions of transport were bounded by the test program. Additional testing was performed for safe interim storage.
Transportation tests of 30 ft top and side impact drops of loaded Pipe Overpack Containers, were performed. The drop tests simulated the interaction effects of other fully loaded Pipe Overpack Containers within a TRUPACT-II.
The transportation testing consisted of:
The site storage testing consisted of:
A helium leak test was one of the methods used to determine if the Pipe Component passed or failed the tests. The Pipe Components used in the tests were fitted with leak test ports to allow connection to the leak detector. To facilitate this test, the outlet ports of the filters were sealed with vacuum putty or a clamping fixture, which allowed the gasket between the filter and the Pipe Component to be tested. After the tests, the filters were removed, and an evaluation of the filter performance was conducted by the filter manufacturer.
There was no loss of containment in any drop or crush tests. All Pipe Components had a leakage rate of less than 1.times.10.sup.-7 cm.sup.3 /s. The filters showed no damage from the drop and crush tests. They were verified to have met flow and filtering requirements.
The engulfing pool fire test had mixed results. With one exception, all Pipe Components were found to be leak tight after the fire test. One Pipe Component was found to have a helium leak rate of approximately 24 cm.sup.3 /s after the fire test where leakage was detected between the lid and the weld neck flange and between the filter and the lid. The drum which contained this unit had the stainless steel-housed filter rather than the polyethylene filter. During the fire test, this drum became sufficiently pressurized to blow off the drum lid. At this point, the Pipe Component was exposed directly to the heat from the fire, and the elastomeric O-ring and filter gasket were both destroyed. The polyethylene-housed drum filters installed in the lids of the other three drums melted and were blown out of the drum lid. This provided a pressure relief pathway sufficient enough to prevent the lids from blowing off. Although the containment provided by the drum was compromised, the Pipe Components contained therein retained their integrity and did not leak.
A series of criticality analyses modeled TRUPACT-II payload assemblies of Pipe Overpack Containers to evaluate the highest system "k-effective" value possible. The analyses constructed potential configurations of postulated accident geometries for a payload of Pipe Overpack Containers. The model evaluated a loading of 200 grams of Pu239 per Pipe Overpack Container in both dry and water-saturated forms. The following conservative assumptions were used in the analyses under normal transport conditions and hypothetical accidents:
These assumptions are comparable to those used in the criticality analyses performed for other authorized payload containers with one exception. One key assumption used to analyze the criticality potential and to establish control limits for other payload containers was that all fissile material within the payload containers would breach the packaging to come together under hypothetical accident conditions. The Pipe Component impact testing results demonstrate that the structural integrity of the Pipe Component prevents the release of its contents under hypothetical accident conditions. Thus, the criticality analyses assume no loss of containment by the Pipe Component despite the elimination of the drum, packing material, and any layers of confinement used inside the Pipe Component.
The results of the analysis show that no simulation of TRUPACT-II payload assemblies of Pipe Overpack Containers exceeded an average k-effective value of 0.9. This demonstrates that the system was subcritical in all cases. Therefore, a TRUPACT-II shipment of fourteen Pipe Overpack Containers with 200 FGE each is safe for transportation and meets criticality requirements for transport during normal and hypothetical accident conditions.
The Pipe Overpack Container has been assessed for its radiation shielding. Effective radiation shielding depends on a continuous barrier of dense material (i.e., steel) without openings that would allow radiation "streaming" or leakage. Both Pipe Component designs provide a nominal 1/4 inch of steel for shielding of 60 Kev gamma radiation from Americium (Am241). The Pipe Component has a design feature to prevent radiation streaming through the relatively low density filter media of the filter vents. Puncture protection is also provided to the filter media via the same design.
The Pipe Overpack Container must meet the TRUPACT-II Safety Analysis Report for Packaging (SARP) requirements for dose rate limits. The measured radiation dose rates of each Pipe Overpack Container must comply with the 200 millirem/hour at the container surface and 10 millirem/hour at two meters requirement. It is estimated that the worst case loading using the Pipe Overpack Container will produce no more than 10 millirem/hour combined gamma and neutron at the surface of the container.
Finite element modeling was used to support analysis of the Pipe Overpack Container to resolve storage accident scenarios where physical testing of the container could not be easily performed. Two scenarios were evaluated. One risk to the integrity of the Pipe Overpack Container during handling and storage is an accident where the Pipe Overpack Container drum is punctured by the tine of a forklift. The other accident scenario analyzed involves the collapse of the roof of a storage building.
The forklift accident scenario assumed a 4920 kg forklift traveling at 4.5 m/s pinning the Pipe Overpack Container against a rigid wall. The impacting position of the tine was chosen to maximize damage of the Pipe Component. Both the 6 and 12 inch diameter Pipe Components were capable of stopping the forklift without a total failure of the component. The pipes were bent significantly but remained relatively intact. The strain concentrations caused when the outside tip of the tine impacted the pipe were high enough to assume that localized tearing of the pipe wall would occur at this location. The design of the tine used in the analyses had a squared off end which greatly contributed to the strain concentration.
A slightly off-center impact was analyzed to determine whether it was a more severe impact than the symmetrical impact conditions. The ability of the Pipe Component to move away from the tine was effective at keeping the strains in the Pipe Component to below the failure strain limits.
The building collapse scenario evaluated the collapse of the roof structure of the storage building onto the Pipe Overpack Container. Three possible impact orientations were selected for the analysis: a flat section of roof impacting the top of the Pipe Overpack Container, a flat section of roof impacting the side of the container, and the edge of a roof section impacting the side of the container. In all of these analyses, the roof section was assumed to be rigid and traveling at constant velocity. The amount of energy absorbed by the package at its failure point was calculated which allowed the risk assessment to determine the weight of a roof section necessary to cause the package to fail.
In a real accident, it is possible that more than one container will be impacted by the collapsing roof structure. Under these conditions, the total energy absorbed will be equal to energy absorbed by each package times the number of packages impacted by the falling roof structure. The amount of energy absorbed by a single package gives an indication of how massive a roof section can fall from a given height without causing package failure. From the analysis, a single 6 inch Pipe Overpack Container in an end impact orientation implies that this package would not fail if impacted by a 2950 kg roof section falling from 6.1 m. For a 10.2 cm thick reinforced concrete slab, this equates to a section more than 3.65 meter square. For the impact of an edge of a roof section onto the side of the 12 in. Pipe Overpack Container, the absorbed energy is equal to a 232 kg roof section falling from 6.1 m. For a 10.2 cm thick roof slab, this weight is equal to a 1.06 meter square section. The edge of a roof section falling on the side of a 12 inch Pipe Overpack Container in its most vulnerable location is the most damaging case.
The development, testing, and approval of the Pipe Overpack Container have resulted in its approval for use. Utilization of the Pipe Overpack Container results in substantial optimization of packaging transuranic wastes and their shipment to an approved disposal site. It further reduces the risks to the workers and the public.
Thus, it is an object of this invention to provide an inner container for use with a Nuclear Regulatory Commission (NRC) approved type B outer container, in the current enablement a TRUPACT-II, to transport transuranic waste.
It is a further object of this invention to provide an inner container for use with an NRC approved type B outer container for the transport of transuranic waste material where the inner container provides radiation shielding to allow for the transportation of waste material having a high Americium-241 content.
It is a further object of this invention to provide an inner container for use with an NRC approved type B outer container for the storage of transuranic waste material where the inner container provides radiation shielding.
Finally, it is an object of this invention to provide for an inner container for use with an NRC approved type B outer container for the transportation and storage of highly dispersible materials containing plutonium.
Additional advantages, objects and novel features of the invention will become apparent to those skilled in the art upon examination of the following and by practice of the invention.